Interpenetration Phenomena via Anion Template Effects in Fe(II) and Co(II) Coordination Networks with a Bis-(1,2,4-triazole) Ligand

Seven new coordination networks, [Fe(tbbt)3](BF4)2 (1), [Co(tbbt)3](BF4)2 (2), [Fe(tbbt)3](ClO4)2 (3), [Co(tbbt)3](ClO4)2 (4), [Fe(NCS)2(tbbt)2] (5), [Co(NCS)2(tbbt)2] (6), and [Fe(H2O)2(tbbt)2]Br2·2H2O (7), were synthesized with the linker 1,1’-(trans-2-butene-1,4-diyl)bis-1,2,4-triazole (tbbt) and structurally investigated. The structure of complexes 1–4 is composed of three interpenetrating, symmetry-related 3D networks. Each individual 3D network forms a primitive, nearly cubic lattice (pcu) with BF4– or ClO4– anions present in the interstitial spaces. The structure of compounds 5 and 6 is composed of two-dimensional sql layers, which are parallel to each other in the AB stacking type. These layers are interpenetrated by one-dimensional chains, both having the same formula unit, [M(NCS)2(tbbt)2] (M = Fe, Co). The structure of compound 7 consists of parallel, two-dimensional sql layers in the ABCD stacking type. The interpenetration in 1–6 is not controlled by π–π-interactions between the triazole rings or C=C bonds, as could have been expected, but by (triazole)C-H⋯F4B, C-H⋯O4Cl, and C-H⋯SCN anion hydrogen bonds, which suggests a template effect of the respective non-coordinated or coordinated anion for the interpenetration. In 7, the (triazole)C-H⋯Br anion interactions are supplemented by O-H⋯O and O-H⋯Br hydrogen bonds involving the aqua ligand and crystal water molecules. It is evident that the coordinated and non-coordinated anions play an essential role in the formation of the networks and guide the interpenetration. All iron(II) coordination networks are colorless, off-white to yellow-orange, and have the metal ions in the high-spin state down to 77 K. Compound 5 stays in the high spin state even at temperatures down to 10 K.


Introduction
According to the IUPAC definition, coordination polymers consist of repeating coordination entities extending in one, two, or three dimensions [1][2][3]. Controlling their structure, thus leading to the desired properties for potential applications, can be described as one of the greatest goals of supramolecular chemistry in general [4,5]. Among the promising ways to achieve specific topologies and structures are self-assembly processes involving metal pixel array detector and a micro-focus sealed X-ray tube, PhotonJet (Cu) X-ray source (λ = 1.54184 Å). CRYSALISPRO was used for cell refinement, data reduction, and absorption correction [67]. The crystal structure was solved using OLEX2 with SHELXT, and the refinement was done with SHELXL [68][69][70]. Figures were drawn with DIAMOND 4.0 software [71]. The values for the distortion indices of the coordination polyhedra of 1-7 were calculated using OctaDist software [72]. For further information, see Supplementary Materials, Section S7.
SCO experiments were carried out as follows: single crystals of compounds 1-7 were selected and mounted with oil on a cryo-loop. The single crystals were cooled down to 80 K using the cryocooler of a Rigaku XtaLAB Synergy S diffractometer (Rigaku, Tokyo, Japan) at a rate of 0.5 K/min.
The temperature-dependent magnetic susceptibility of compound 5 was recorded using a Quantum Design SQUID magnetometer MPMS-XL7 (Quantum Design, San Diego, CA, USA). Measurements were made in a temperature range of 10 K to 300 K and under an applied external field of 0.1 Tesla. The temperature-dependent magnetic moments were corrected for the diamagnetic contribution of the holder, as well as for the diamagnetic contribution of the sample, which was determined using the Pascal constant.
For powder pressure experiments, powders of compounds 1-7 were pressed with a 30-ton press, a P30 hydraulic press by Research Industrial Instrument Co. (London, England), under vacuum in a 13 mm press tool for KBr pellets by the LOT-Oriel Group (LOT-Oriel Group, Darmstadt, Germany) at a pressure of 9 t for 10 min.
The synthesis of the metal-tbbt networks 1-7 is schematically presented in Scheme 1. Compounds 1-4 were initially synthesized with both 1:2 and 1:3 molar metal:ligand ratios. Even at the experimental M:L ratio of 1:2, the structures of 1-4 with an M:L formula ratio of 1:3 were obtained, as verified by identical powder X-ray diffractograms. However, at the ratio of 1:3, the quality of the single crystals for the X-ray analysis was usually better. The synthesis of 1-4 and 6 proceeds by the straightforward reaction of the metal salts and the tbbt linker in water. The synthesis of compound 5 includes the combination of three separately heated solutions of the metal salt, NH 4 SCN, and linker. The synthesis of 7 includes the in situ formation of an intermediary product (ferrous nitrate) [76] at elevated temperature before the addition of tbbt. The combination of hot solutions in the case of 5-7 was necessary to avoid the rapid precipitation of 5-7 as powders, instead of the formation of single crystals upon slow cooling (Scheme 1). Images of the single crystals can be found in Supplementary Materials, Section S5. The colorless, off-white to yellow-orange color of the iron products and the yellow to orange color of the cobalt compounds signals their HS state [25].  [77]. Due to structural similarities, the IR spectra of 1-4 or 5 and 6, respectively, look almost identical.
Thermogravimetric analysis indicates a thermal stability of at least 250 °C for 1-6 and around 80 °C for 7 (see Supplementary Materials, Section S4). The main thermal decomposition step for 1-7 is attributed to the decomposition of the tbbt linker. The neat tbbt compound decomposes between ~180 and 280 °C at a heating rate of 5 K min −1 ( Figure  S4). As a linker in the metal complexes 1-7, the decomposition starts at ~250 °C or even later, indicating a thermal stabilization upon metal coordination caused by rigidification of the molecule. The BF4 -compounds 1 and 2 (dec. from ~300 °C, Figures S12 and S13) or the NCS compounds 5 and 6 (dec. starting ~250 °C, Figures S16 and S17) show almost similar stabilities and TGA traces. Decomposition of the BF4 -anion leads to FeF3 in 1, CoF2 in 2, FeS2 in 5, and CoS2 in 6, whose mass fractions are close to the residual mass-% values at 600 °C. Perchlorate compounds 3 and 4 both undergo sudden sharp mass loss because of an explosive decomposition at about 250 °C and 340 °C, respectively (Figures S14 and S15). Please note our warning that perchlorate salts are potentially explosive and must be handled with care! The first decomposition step in 7 is due to the loss of the four water molecules, while the second step at above 300 °C is attributed to the ligand ( Figure S18).
The pH stability of each compound was visually checked in an aqueous medium for one hour. Iron compounds 1, 3, 5, and 7 are stable within a range of pH 4 to 6, while the cobalt analogues 2, 4, and 6 are stable between pH 1 and 8. Below pH 3 and above pH 7, the crystals of the iron compounds very quickly turned from almost colorless to green. The cobalt compounds turn blue above pH 8 but retain their faint yellow-orange color down to pH 1.
The topology of the metal-linker networks was elucidated by single-crystal X-ray analysis as presented below. Additional crystal data and values of the distortion of the metal coordination polyhedra of 1-7 can be found in the Suppl. Mater., Sections S6 and S7. Additional structure images are provided in the Supplementary Materials, Section S8.  [77]. Due to structural similarities, the IR spectra of 1-4 or 5 and 6, respectively, look almost identical.
Thermogravimetric analysis indicates a thermal stability of at least 250 • C for 1-6 and around 80 • C for 7 (see Supplementary Materials, Section S4). The main thermal decomposition step for 1-7 is attributed to the decomposition of the tbbt linker. The neat tbbt compound decomposes between~180 and 280 • C at a heating rate of 5 K min −1 ( Figure  S4). As a linker in the metal complexes 1-7, the decomposition starts at~250 • C or even later, indicating a thermal stabilization upon metal coordination caused by rigidification of the molecule. The BF 4 compounds 1 and 2 (dec. from~300 • C, Figures S12 and S13) or the NCS compounds 5 and 6 (dec. starting~250 • C, Figures S16 and S17) show almost similar stabilities and TGA traces. Decomposition of the BF 4 anion leads to FeF 3 in 1, CoF 2 in 2, FeS 2 in 5, and CoS 2 in 6, whose mass fractions are close to the residual mass-% values at 600 • C. Perchlorate compounds 3 and 4 both undergo sudden sharp mass loss because of an explosive decomposition at about 250 • C and 340 • C, respectively (Figures S14 and S15). Please note our warning that perchlorate salts are potentially explosive and must be handled with care! The first decomposition step in 7 is due to the loss of the four water molecules, while the second step at above 300 • C is attributed to the ligand ( Figure S18).
The pH stability of each compound was visually checked in an aqueous medium for one hour. Iron compounds 1, 3, 5, and 7 are stable within a range of pH 4 to 6, while the cobalt analogues 2, 4, and 6 are stable between pH 1 and 8. Below pH 3 and above pH 7, the crystals of the iron compounds very quickly turned from almost colorless to green. The cobalt compounds turn blue above pH 8 but retain their faint yellow-orange color down to pH 1.
The topology of the metal-linker networks was elucidated by single-crystal X-ray analysis as presented below. Additional crystal data and values of the distortion of the metal coordination polyhedra of 1-7 can be found in the Supplementary Materials, Sections S6 and S7. Additional structure images are provided in the Supplementary Materials, Section S8. For each compound powder, X-ray diffraction patterns positively matched the corresponding simulated pattern from the single-crystal X-ray analysis and, thereby, supported the phase purity of each compound (see Supplementary Materials, Section S9). Crystallographic X-ray analysis shows compounds 1-4 to be isostructural, all crystallizing in the trigonal space group P3. The asymmetric unit contains one M(II) atom (M = Fe, Co) (residing on an inversion center and a threefold rotation axis), one half-linker molecule (inversion center at the middle of the C=C bond) and half a BF 4 -or ClO 4 anion on the threefold rotation axis with one of the B-F or Cl-O bonds coinciding with the rotation axis ( Figure 1). The F and O atoms of the anion in 2-4 are slightly disordered, as indicated by the transparent F or O atoms in Figure 1. The octahedral coordination sphere of each Fe(II) and Co(II) metal ion is composed of six symmetry-related nitrogen donor atoms from six triazole rings of six tbbt molecules ( Figure 1) and is only negligibly distorted (see Supplementary Materials, Section S7). For each compound powder, X-ray diffraction patterns positively matched the corresponding simulated pattern from the single-crystal X-ray analysis and, thereby, supported the phase purity of each compound (see Suppl. Mater., Section S9).

Crystal Structures of [M(tbbt)3](BF4)2 and [M(tbbt)3](ClO4)2 (M = Fe 1, 3; M = Co 2, 4)
Crystallographic X-ray analysis shows compounds 1-4 to be isostructural, all crystallizing in the trigonal space group P3 ̅ . The asymmetric unit contains one M(II) atom (M = Fe, Co) (residing on an inversion center and a threefold rotation axis), one half-linker molecule (inversion center at the middle of the C=C bond) and half a BF4 -or ClO4 -anion on the threefold rotation axis with one of the B-F or Cl-O bonds coinciding with the rotation axis ( Figure 1). The F and O atoms of the anion in 2-4 are slightly disordered, as indicated by the transparent F or O atoms in Figure 1. The octahedral coordination sphere of each Fe(II) and Co(II) metal ion is composed of six symmetry-related nitrogen donor atoms from six triazole rings of six tbbt molecules ( Figure 1) and is only negligibly distorted (see Supplementary Materials, Section S7).
Two crystallographically equivalent metal(II) atoms are connected by one ligand molecule to establish a three-dimensional (3D) network, which forms a primitive, almost cubic lattice (pcu) with two non-coordinated anions on each face (Figure 2a). The M···M distance along the connecting tbbt linker is between 13.9 Å and 14.0 Å . In view of the long linker and, consequently, large void space in a single 3D network, three such symmetry- The Fe-N bond lengths are 2.186(2) Å in 1 and 2.191(2) Å in 3, which is the typical range of an iron(II) high-spin complex [26,75,78]. The Co-N bond lengths with 2.149(2) Å in 2 and 2.150(2) Å in 4 are also in the range of a cobalt(II) high-spin complex [78,79].

Crystal structures of [M(NCS)2(tbbt)2] (M = Fe 5; M = Co 6)
The isostructural compounds 5 and 6 crystallize in the triclinic space group P1 ̅ . The asymmetric unit contains two crystallographically different M(II) atoms (M = Fe, Co), each on an inversion center, one full and two half tbbt molecules (the latter have again an inversion center at the middle of the C=C bond), and a metal-coordinated isothiocyanate anion (Figure 3). Both metal atoms are coordinated in an octahedral fashion by four different tbbt molecules and two trans-positioned isothiocyanate anions [75,78]. Different from the structures of 1-4 where the anions BF4 − and ClO4 − are weakly coordinating and normally do not coordinate to metal atoms, the well-ligating NCSanions coordinate through the N atom as isothiocyanate ligands to the metal atoms. Thus, for the six- tbbt molecules and two trans-positioned isothiocyanate anions [75,78]. Different from the structures of 1-4 where the anions BF 4 − and ClO 4 − are weakly coordinating and normally do not coordinate to metal atoms, the well-ligating NCSanions coordinate through the N atom as isothiocyanate ligands to the metal atoms. Thus, for the six-coordinated metal atoms, only four donor atoms have to come from the tbbt molecules so that a 3D metallinker network will not be feasible anymore-at most, only a 2D network. The coordination sphere for the M2 atom is slightly more distorted than for M1 (see Supplementary Materials, Section S7).
Polymers 2023, 15, x FOR PEER REVIEW 9 of coordinated metal atoms, only four donor atoms have to come from the tbbt molecules that a 3D metal-linker network will not be feasible anymore-at most, only a 2D netwo The coordination sphere for the M2 atom is slightly more distorted than for M1 (s Supplementary Materials, Section S7).  [26,75,78]. In 6, the Co-NCS bond length is 2.110(2) Å a Co-N(triazole) 2.158(2) Å , both also indicating the HS state [78,79].

Crystal Structure of [Fe(H2O)2(tbbt)2]Br2· 2H2O (7)
Using bromide as the counter anion, a different structure motif was obtained. Compound 7 crystallizes in the orthorhombic space group Fdd2. The asymmetric unit contains one-half of an octahedrally coordinated iron(II) atom (on a twofold rotation axis), one full linker molecule, two halves of Fe-coordinated water molecules (aqua ligands), one non-coordinated crystal water molecule, and a bromine anion ( Figure 5). In contrast to compounds 1-4 and similar to compounds 5 and 6, the metal ion in compound 7 is only coordinated by four nitrogen donor atoms. Hence, a 3D framework cannot form, only a 2D metal-linker network. The potentially coordinating Branion does not bind to iron and engages only in hydrogen bonding. Possibly, the coordination of the harder aqua ligand and the non-coordination of the softer bromine can be rationalized by the hard and soft acid and base concept if the Fe(II) ion is categorized on the harder acid site [91][92][93]. The distortion of the octahedral coordination environment is stronger compared to compounds 1-6 (see Supplementary Materials, Section S7).

Crystal Structure of [Fe(H 2 O) 2 (tbbt) 2 ]Br 2 ·2H 2 O (7)
Using bromide as the counter anion, a different structure motif was obtained. Compound 7 crystallizes in the orthorhombic space group Fdd2. The asymmetric unit contains one-half of an octahedrally coordinated iron(II) atom (on a twofold rotation axis), one full linker molecule, two halves of Fe-coordinated water molecules (aqua ligands), one non-coordinated crystal water molecule, and a bromine anion ( Figure 5). In contrast to compounds 1-4 and similar to compounds 5 and 6, the metal ion in compound 7 is only coordinated by four nitrogen donor atoms. Hence, a 3D framework cannot form, only a 2D metal-linker network. The potentially coordinating Branion does not bind to iron and engages only in hydrogen bonding. Possibly, the coordination of the harder aqua ligand and the non-coordination of the softer bromine can be rationalized by the hard and soft acid and base concept if the Fe(II) ion is categorized on the harder acid site [91][92][93]. The distortion of the octahedral coordination environment is stronger compared to compounds 1-6 (see Supplementary Materials, Section S7).
In 7, corrugated sql layers are formed with a syn conformation of the linker (Figure  6a), whereas in 1-6, the tbbt linker was bridging the metal atoms in the networks with its anti-conformation (only the chains in 5 and 6 had the linker bridge in syn-conformation). In 7, the syn conformation is responsible for the layer corrugation. Hence, in 7, the Fe···Fe distance of 9.6 Å within the layer is considerably smaller than the approximately 14 Å in the 3D networks in 1-4 and in the layers in 5-6 but is as seen in the chains in 5-6. Consequently, no interpenetration or polycatenation occurs with the layers in 7; instead, each pore in the layer is filled with four water molecules and two bromine anions ( Figure  6b). These corrugated layers are arranged in an ABCD stacking type with a distance of 7.7 Å between the layer planes as defined by the Fe atoms (Figure 6c). This distance is almost 1.4 Å larger than in 5 and 6. The different layers interdigitate because of their corrugated nature (Figure 6d). The hydrogen bond length between the coordinated and noncoordinated water molecules is 1.94(5) Å . The O-H···Br hydrogen bonds are between 2.48(4) Å and 2.61(4) Å . The (triazole)C-H···Br hydrogen bonds are 2.83(5) Å and 2.86(5) Å.
In 7, corrugated sql layers are formed with a syn conformation of the linker (Figure 6a), whereas in 1-6, the tbbt linker was bridging the metal atoms in the networks with its anti-conformation (only the chains in 5 and 6 had the linker bridge in syn-conformation). In 7, the syn conformation is responsible for the layer corrugation. Hence, in 7, the Fe· · · Fe distance of 9.6 Å within the layer is considerably smaller than the approximately 14 Å in the 3D networks in 1-4 and in the layers in 5-6 but is as seen in the chains in 5-6. Consequently, no interpenetration or polycatenation occurs with the layers in 7; instead, each pore in the layer is filled with four water molecules and two bromine anions (Figure 6b). These corrugated layers are arranged in an ABCD stacking type with a distance of 7.7 Å between the layer planes as defined by the Fe atoms (Figure 6c). This distance is almost 1.4 Å larger than in 5 and 6. The different layers interdigitate because of their corrugated nature (Figure 6d). The hydrogen bond length between the coordinated and non-coordinated water molecules is 1.94(5) Å. The O-H· · · Br hydrogen bonds are between 2.48(4) Å and 2.61(4) Å. The (triazole)C-H· · · Br hydrogen bonds are 2.83(5) Å and 2.86(5) Å.

Spin-Crossover Properties
The LS state is enthalpically favored, hence more stable at lower temperatures, while the HS state is entropically favored and, therefore, more stable at higher temperatures [26]. Given that Fe(II) triazole complexes are known to be thermochromic, with a reddish-purple color in the LS state, compounds 1-7 were cooled from room temperature down to 77 K by immersing the vials containing off-white to yellow-orange samples into liquid nitrogen, but no color change was observed.
Considering the possibility of the occurrence of a so-called thermally induced excited spin-state trapping effect (TIESST effect), which describes a metastable HS state at low or even cryogenic temperatures on fast cooling [28,30,40,94,95], we even used a relatively low cooling rate (0.5 K/min) down to 80 K using the cryo-cooler device on the single-crystal X-ray diffractometer, but no SCO was observed. 6b). These corrugated layers are arranged in an ABCD stacking type with a distance of 7.7 Å between the layer planes as defined by the Fe atoms (Figure 6c). This distance is almost 1.4 Å larger than in 5 and 6. The different layers interdigitate because of their corrugated nature (Figure 6d). The hydrogen bond length between the coordinated and noncoordinated water molecules is 1.94 (5)

Spin-Crossover Properties
The LS state is enthalpically favored, hence more stable at lower temperatures, while the HS state is entropically favored and, therefore, more stable at higher temperatures [26]. Given that Fe(II) triazole complexes are known to be thermochromic, with a reddishpurple color in the LS state, compounds 1-7 were cooled from room temperature down to 77 K by immersing the vials containing off-white to yellow-orange samples into liquid nitrogen, but no color change was observed.
Considering the possibility of the occurrence of a so-called thermally induced excited spin-state trapping effect (TIESST effect), which describes a metastable HS state at low or even cryogenic temperatures on fast cooling [28,30,40,94,95], we even used a relatively low cooling rate (0.5 K/min) down to 80 K using the cryo-cooler device on the singlecrystal X-ray diffractometer, but no SCO was observed.
One explanation for a non-existing SCO in 1-7 could be that the SCO occurs at lower temperatures or is blocked by the strong rigidity of the networks, which prevent the significant shrinking of the iron(II) nitrogen bond lengths in the LS state. Another reason for the missing SCO could be the present distortion of the metal coordination sphere (see Supplementary Materials, Section S7), which can play a significant role in the stabilization of the LS state [96][97][98][99].
To test these assumptions, compound 5, potentially the most structurally flexible of the iron compounds, was cooled even further to 10 K while performing SQUID measurements of the magnetic susceptibility (Figure 7). One explanation for a non-existing SCO in 1-7 could be that the SCO occurs at lower temperatures or is blocked by the strong rigidity of the networks, which prevent the significant shrinking of the iron(II) nitrogen bond lengths in the LS state. Another reason for the missing SCO could be the present distortion of the metal coordination sphere (see Supplementary Materials, Section S7), which can play a significant role in the stabilization of the LS state [96][97][98][99].
To test these assumptions, compound 5, potentially the most structurally flexible of the iron compounds, was cooled even further to 10 K while performing SQUID measurements of the magnetic susceptibility ( Figure 7).
However, even cooling to 10 K did not result in spin switching, and the compound remained in the high-spin state over the entire temperature range, suggesting that the network is still too rigid to allow SCO. A slight increase in the χ M T value is observed upon cooling to about 50 K, indicating a weak ferromagnetic interaction. The decrease with further temperature decrease can be explained by weak intermolecular antiferromagnetic interactions and/or zero-field-splitting and/or saturation of the magnetization. However, even cooling to 10 K did not result in spin switching, and the compound remained in the high-spin state over the entire temperature range, suggesting that the network is still too rigid to allow SCO. A slight increase in the χMT value is observed upon cooling to about 50 K, indicating a weak ferromagnetic interaction. The decrease with further temperature decrease can be explained by weak intermolecular antiferromagnetic interactions and/or zero-field-splitting and/or saturation of the magnetization.
Since pressure can increase the ligand field strength at the metal center by shortening the metal-ligand bond lengths, provided there is no change in the coordination polyhedron, it is well known that pressure can induce spin-crossover from the HS to the LS state [25,40,100,101]. Such a pressure-induced SCO remains less investigated because of the more challenging experimental requirements. We have thus examined the spin state of 1-7 under pressure [100,101]. Indeed, we were able to observe a color change from colorless to purple for compound 5. While single crystals of 5 switched back to colorless after removing the pressure, a powder of 5 kept the purple color ( Figures S34 and S35). SQUID measurements of this purple powder do not indicate any spin transition ( Figure  S36). A possible explanation for this color change could be a partial oxidation of iron(II) to iron (III) and/or valence tautomerism.
The use of BF4 − or ClO4 − metal salts with weakly coordinating anions leads to the formation of triply interpenetrated 3D pcu lattices (1-4). As the BF4 − or ClO4 − anions do not coordinate to the metal atoms, their close-to-octahedral coordination sphere consists of nitrogen donor atoms from six different bridging tbbt linkers, thereby providing 3D frameworks. Structure and interpenetration are not controlled by interactions between the triazole rings or double bonds, as expected, but by (triazole)C-H···F4B and CH···O4Cl hydrogen bonds through a template effect of the non-coordinated BF4 -or ClO4 -anions. In compounds 5 and 6, the used SCNis coordinated directly to the metal center, with only four N atoms from four tbbt linkers coordinating to the metal atoms. Consequently, these two structures are built of 2D sql layers and 1D double-bridged chains. The 2D layers are interpenetrated by the 1D chains, with the interpenetration again controlled and stabilized by hydrogen bonds from the linkers of the chains to the isothiocyanate groups in the layers. Thus, both in 1-4 and in 5 and 6, the anions exert an interpenetration-guiding template effect. When Bris used as a counter ion, like in 7, non-interpenetrated sql layers in an ABCD stacking type are obtained. In contrast to 1-6, the metal center is coordinated Since pressure can increase the ligand field strength at the metal center by shortening the metal-ligand bond lengths, provided there is no change in the coordination polyhedron, it is well known that pressure can induce spin-crossover from the HS to the LS state [25,40,100,101]. Such a pressure-induced SCO remains less investigated because of the more challenging experimental requirements. We have thus examined the spin state of 1-7 under pressure [100,101]. Indeed, we were able to observe a color change from colorless to purple for compound 5. While single crystals of 5 switched back to colorless after removing the pressure, a powder of 5 kept the purple color ( Figures S34 and S35). SQUID measurements of this purple powder do not indicate any spin transition ( Figure S36). A possible explanation for this color change could be a partial oxidation of iron(II) to iron (III) and/or valence tautomerism.
The use of BF 4 − or ClO 4 − metal salts with weakly coordinating anions leads to the formation of triply interpenetrated 3D pcu lattices (1-4). As the BF 4 − or ClO 4 − anions do not coordinate to the metal atoms, their close-to-octahedral coordination sphere consists of nitrogen donor atoms from six different bridging tbbt linkers, thereby providing 3D frameworks. Structure and interpenetration are not controlled by interactions between the triazole rings or double bonds, as expected, but by (triazole)C-H· · · F 4 B and CH· · · O 4 Cl hydrogen bonds through a template effect of the non-coordinated BF 4 or ClO 4 anions. In compounds 5 and 6, the used SCNis coordinated directly to the metal center, with only four N atoms from four tbbt linkers coordinating to the metal atoms. Consequently, these two structures are built of 2D sql layers and 1D double-bridged chains. The 2D layers are interpenetrated by the 1D chains, with the interpenetration again controlled and stabilized by hydrogen bonds from the linkers of the chains to the isothiocyanate groups in the layers. Thus, both in 1-4 and in 5 and 6, the anions exert an interpenetration-guiding template effect. When Bris used as a counter ion, like in 7, non-interpenetrated sql layers in an ABCD stacking type are obtained. In contrast to 1-6, the metal center is coordinated by four nitrogen atoms of linker molecules and two water molecules, instead of six nitrogen atoms. The bromine anion does not coordinate to the iron atoms. Instead, the presence of hydrogen-bonded Br − and water molecules in the openings of the sql layers prevent any interpenetration in 7.
From the existing interpenetration-guiding template effects and various structural motifs, it was evident in this work that the coordinated and non-coordinated anions play an essential role in the formation of the corresponding networks.
SCO is not observable in any compound. The color change of 5 to purple under pressure seems not to correlate with any spin transition. To understand this behavior, further experiments will follow in subsequent research.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author. The CCDC numbers 2280632-2280638 for 1-7 contain the supplementary crystallographic data reported in this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif (accessed on 30 July 2023).